# PC237 Optics Laboratory

This is the Physics 237 Lab page, created and updated by Terry Sturtevant .
Page last updated Thursday March 15, 2018
**Items marked this way are not final.**

Week 1, Week 2, Week 3, Week 4, Week 5, Week 6, Week 7, Week 8, Week 9, Week 10, Week 11, Week 12

## Evaluation Methods

Many optical properties can be determined in different ways.
For instance, the critical angle can be found in two ways, namely:
1. where the refracted angle is 90°
2. where the reflected light intensity is greater than 0
The Brewster angle can be found in three ways, namely:
1. where the refracted angle is perpendicular to the reflected angle
2. where the reflected light intensity is a minimum
3. where the reflected light is totally polarized
Furthermore, many properties are related to others. In particular, both the critical angle and the Brewster angle are related to the index of refraction.
In this lab, you are going to design an experiment to measure one of those angles. You're then going to test it.
After that you will refine it or try another method of determining it.
You'll then do the same thing for the other angle.
Finally, you'll compare the values from the index of refraction given by the two (or more) methods.
If you don't think you can improve on one or both of your methods, you can also measure the normal incidence reflectivity of the material since it is also related to the index of refraction.

### Week 1: Introduction

In the lab: Optical effects exercise
For next week: Look up each term in question, (i.e. critical angle, Brewster angle, normal incidence reflectivity), and write a description of what it means and a couple of sentences indicating the general principle for measuring it.
In the lab you will attempt to find equipment you can use for the purpose and try it out.

### Week 2: Experiment prep

Pick one of the angles, and examine the equipment in the lab to come up with an experiment for measuring it one way.
For next week: Write up a procedure for doing the experiment and bring it to the lab with you.

### Week 3: Perform experiment

Perform the experiment you devised.
For next week: Write up a lab report for the experiment and bring it to the lab with you.

### Week 4: Experiment prep

Hand in lab report from last week.
For the other angle, examine the equipment in the lab to come up with an experiment for measuring it one way.
For next week: Write up a procedure for doing the experiment and bring it to the lab with you.

### Week 5: Perform experiment

Perform the experiment you devised for measuring it.
For next week: Write up a lab report for the experiment and bring it to the lab with you.

Tips based on the first lab report:
1. Write the "Methods" section in the past tense, not in point form. You are describing what you did, not what the reader should do.
Make sure to include at least one diagram. Would you be able to picture someone else's setup from a text description alone?
2. Show sample calculations in your "Results" since it's often not obvious how to get from your data to your calculated results and uncertainties.
3. In your "Discussion", if you suggest a possible source of error, place bounds on the size of effect it could have.
4. Make sure you actually state the value you got for the thing you set out to measure with its uncertainty in your "Conclusions".
5. Hand in one report for each person in a group.
6. When you revise an experiment, attach the original report along with the revised one.

### Week 6: Revised experiment prep

Hand in lab report from last week.
Figure out how to improve the first experiment you did. This can be either by changing the way you did the original experiment, or by devising a new experiment to measure it one of the other ways.

Some options for improving/changing the first experiment:
1. If you didn't actually determine a value for the angle you were finding, make sure you do that. Also make sure to determine the index of refraction from that.
2. If you only did a single trial, do more.
3. If you used a single sample, repeat for a different sample (or samples) to see if you can measure a difference.
4. If you there is more than one way to identify when you have found a specific angle, and you used only one, then use the other (or an other) way.

For next week: Write up a procedure for doing the experiment and bring it to the lab with you.

### Week 7: Perform experiment

Perform the experiment you devised for measuring it.
For next week: Write up a lab report for the experiment and bring it to the lab with you. Be sure to discuss whether/how the improvements you proposed worked.

Some tips for the lab report:
1. Remember to attach the first lab report to your new one.
2. Since your original report will be attached, you can draw attention to what changes you made to the original experiment.
3. In your Introduction, Methods, and Results, if there was anything not explained or poorly explained in the original, you can clarify.
4. In your Discussion, you can address whether and how your revised experiment improved on the original.
5. In your Conclusions, you can compare your results for the revised experiment to those in the original.

### Week 8: Revised experiment prep

Hand in lab report from last week.
Figure out how to improve the second experiment you did. This can be either by changing the way you did the original experiment, or by devising a new experiment to measure it one of the other ways.
Alternative: If your second experiment worked out well, and you don't need to revise it, you can explore something else.
For next week: Write up a procedure for doing the experiment and bring it to the lab with you.

### Week 9: Perform experiment

Perform the experiment you devised for measuring it.
For next week: Write up a lab report for the experiment and bring it to the lab with you. Be sure to discuss whether/how the improvements you proposed worked.
If you want, you can go ahead and complete the requirements for next week as well.

### Week 10: Compare and combine results

Hand in lab report from last week.
Write up a comprehensive lab report that calculates that index of refraction from each of the experiments, (Brewster angle and critical angle), and compares the values. Many sections can be mostly cut-and-paste from your previous reports.
1. Introduction can have one part for each.
2. Methods can have one part for each.
3. Results can have one part for each.
4. Discusssion will be different. It can start with a section on sources of uncertainty common to both experiments. After that, it needs to have a section about comparing the two experiments as methods of determining the index of refraction. Discuss whether either of the experiments stood out as a better way to determine the index of refraction. For instance:
• Was one method easier to perform?
• Did one method give more consistent results?
• If you used different materials in the different experiments, did the index values from both fall within expectations?
5. Conclusions should give you best value for the index of refraction, based on the discussion above, and indication of whether or not it agreed with expectations.

### Week 11: Submit final report

Hand in report from last week.

### Week 12

Get marked report from last week.

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